#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>

#define MAXOP 100
#define NUMBER '0'

int getop(char []);
void push(double);
double pop(void);
void ungetch(int c);
int getch(void);

int main()
{
    int type;
    double op2;
    char s[MAXOP];

    while((type = getop(s)) != EOF){
        switch (type)
        {
        case NUMBER:
            push(atof(s));
            break;
        case '+':
            push(pop() + pop());
            break;
        case '*':
            push(pop() * pop());
            break;
        case '-':
            op2 = pop();
            push(pop() - op2);
            break;
        case '/':
            op2 = pop();
            if(op2 != 0.0)
                push(pop() / op2);
            else
                printf("error: zero divisor\n");
            break;
        case '%':
            op2 = pop();
            if(op2 != 0.0)
                push((int)pop() % (int)op2);
            else
                printf("error: zero divisor\n");
            break;
        case '\n':
            printf("\t%.8g\n", pop());
            break;                
        default:
            printf("error: unknown command %s\n", s);
            break;
        }
    }
    return 0;
}

#define MAXVAL 100
int sp = 0;
double val[MAXVAL];
void push(double f)
{
    if(sp < MAXVAL)
        val[sp++] = f;
    else
    {
        printf("error: stack full, can't push %g\n",f);
    }
}

double pop(void)
{
    if(sp > 0)
        return val[--sp];
    else
    {
        printf("error: stack empty\n");
        return 0.0;
    }
}

int getop(char s[])
{
    int i,c;
    while ((s[0]= c = getch()) == ' ' || c == '\t');
    s[1] = '\0';
    if(!isdigit(c) && c != '.')
        return c;
    i = 0;
    if(isdigit(c))
        while (isdigit(s[++i] = c = getch()));
    if(c == '.')
        while (isdigit(s[++i] = c = getch()));
    s[i] = '\0';
    if(c != EOF)
        ungetch(c);
    return NUMBER;            
}

#define BUFSIZE 100
char buf[BUFSIZE];
int bufp = 0;
int getch(void)
{
    return (bufp > 0) ? buf[--bufp] : getchar();
}
void ungetch(int c)
{
    if(bufp >= BUFSIZE)
        printf("ungetch: too many characters\n");
    else
    {
        buf[bufp++] = c;
    }    
}
